1. Field of the Invention
The present invention relates to a data handling system, for example for handling data in a telecommunication system. The present invention is particularly, but not exclusively, concerned with a telecommunications system for mobile telephones.
2. Summary of the Prior Art
When a telecommunication system involves mobile telephones, a call to a mobile telephone is not to a fixed point, and therefore the system must determine the location of the destination. The simplest arrangement is for a call to a mobile telephone to result in a signal being transmitted to a data storage unit in the form of a Home Location Register unit (HLR) which determines the location of the mobile telephone, and so permits routing of the call to occur.
Inevitably, HLRs have a limited capacity, and some arrangement is therefore necessary to enable telecommunication systems to access multiple HLRs. It should be noted that it is also envisaged that users may need multiple MSISDN numbers, for example if a user is to have the possibility of both voice and data communication, in existing systems, any second MSISDN number with a common identity number (IMSI) must be a MSISDN number of the same HLR as the previous MSISDN number. This could be impossible to achieve if, for example, the HLR containing the original information is full. Then the only way that additional services could be provided would require the user to change telephone number, which would be undesirable. This becomes a particular problem if it is desirable that users are able to select their numbers, rather than be provided with them.
WO 96/11557 (corresponding to U.S. Ser. No. 08/809,767) the disclosure of which is herein incorporated by reference, proposed that the switch network which connects users to other users, HLRs, and system services, had a register unit associated therewith, which register unit contained information relating each telephone number to a corresponding one of a plurality of HLRs. The relationship between telephone numbers and HLRs should then be freely selectable within the register unit, so that the register unit acted as a converter between the number and the information identifying the HLR.
By providing such a register unit, the fixed relationship between numbers and HLRs was broken, and any number can be assigned to any HLR, assuming space permits. WO 96/11557 also proposed that the register unit stored further information associated with the mobile telephones which permits the switch network to enable calls from mobile telephones to be routed to different services, depending on the calling mobile telephone itself, in addition to the number dialled. The ideas proposed in WO 96/11557 were then developed further in WO 97/14237 by considering the location within which information is stored in the network.
When considering data in the network, there are two things that need to be taken into account. The first is the storage of the data itself, and the second is data control, being the means of handling queries, updates, results in synchronisation messages and similar controls. The arrangement described in WO 96/11557 can be considered to be of this type in that the register needs to store data, and also needs to store control information for acting on that data.
At first sight, both the data and the data control functions may be located at a single site, and stored on a single physical device such as a server which responds to queries and updates. The information stored may be considered to comprise a data function and a data control function, with the data function representing sets of data relating to respective telephone numbers, telephone control operations, etc. The data function and data control function may be considered to form a database of functions.
However, if there is only a single database that operate in this way, the network is vulnerable to failure. Therefore, WO 97/14237 proposed that the database of functions be replicated a plurality of times. Each database comprises a data function and a data control function. The replicated databases may physically be located in a single location, or may be at a plurality of physically separate locations. In either case, each replicated database may be considered to be a service data function with each such function being a notional site in the network. The sites of the functions are thus virtual sites, rather than being necessarily physically separate.
When considering such a distributed set of functions, it is important for the data functions to be synchronised and the data control functions to interwork to control the synchronisation. This synchronisation includes not only the need for the information about any particular telephone number to be the same at each function, but also for the facilities associated with that telephone number to the same at each function. WO 97/14237 therefore discussed the synchronisation of those functions.
In a telephone network, it is important that any updating of the functions is carried out in real-time, and in a synchronised way. It is not acceptable for the network to be updated gradually, as happens in existing computer database techniques.
WO 17/94237 therefore proposed that, in a network of interconnected functions each of which is to be synchronised, one of those functions was identified as a primary function, at least one other function is identified as a primary standby function, with any remaining function(s) being considered secondary. Then, when updating is needed, the primary function synchronised all other functions by signalling to them an update that it had received. Those other functions then signalled to the primary function that they had acted on the update. The primary function then signalled externally that the update has occurred, and at the same time provided acknowledgement signals to the other functions. If for any reason the primary function failed, the primary standby function may then take over control of the updating operation.